Andreas Schmidt et al.
Organic & biomolecular chemistry, 1(23), 4342-4350 (2003-12-20)
2,3-Diaminophenol 4, 3,4-diaminophenol 5, 4-methoxy-1,2-diaminobenzene 6, 3,4-diaminobenzenethiol 7, 2,3-diaminobenzoic acid 8, and 3,4-diaminobenzoic acid 9 were reacted with 2,4-pentanedione to yield the corresponding benzo[b][1,4]diazepinium salts, respectively. The hydroxy-benzo[b][1,4]diazepinium salts 17 and 18 do not form mesomeric betaines (MB) on deprotonation.